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Mercruiser 3.0 Low Compression

T

Tarks

New member
Changed the plugs today in my 3.0 Mercruiser TKS and checked compression. Getting 160, 135, 95, 145. The low compression in cylinder 3 is concerning. Cylinder 2 is also lower (approx 15 psi) than the last time I checked compression. Boat runs good but sometimes is difficult to start. From what Ive read these motors are known to to have rough starts? Should I be concerned? Does this sound like a possible head gasket? Thanks.
 
with that much difference in compression, the engine isn't making all of the power that it could...

I'd be inclined to do a leakdown test to get a better handle on the source of the problem.
 
Would think if it was head gasket both 2&3 would be equally low. Do the leakdown to see could be a bad valve or misadjusted valves if work was done. Starting is probably carb or ignition related

if this is a saltwater boat would be looking at exhaust/elbow condition if water leaks back into exhaust valves rusting them. Could also burn a valve if its lean… what do spark plugs look like
 
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